Water-washable inspection penetrant employing triglycerides and polyglycerides of fatty acids

ABSTRACT

A water-washable inspection penetrant composition and process in which a low-solubility fatty oil is used as the penetrant vehicle. The solvent liquids of the invention provide enhanced stability of penetrant entrapments in surface flaws, so as to increase the allowable time interval of wash water contact before an excessive depletion of the entrapment occurs. The flaw detecting capability of the water-washable penetrant is thereby improved.

[22] Filed:

United States Patent 11 1 Alburger 1 Dec. 30, 1975 [54] WATER-WASHABLEINSPECTION PENETRANT EMPLOYING TRIGLYCERIDES AND POLYGLYCERIDES OF FATTYACIDS [76] Inventor: James R. Alburger, 5007 Hillard Ave., La Canada,Calif. 91011 21 Appl. No.: 513,084

Related US. Application Data [63] Continuation-impart of Ser. No.482,465, June 24,

Alburger 252/30l.2 P Graham 252/301.2 P

Primary ExaminerJohn H. Mack Assistant Examiner-Aaron Weisstuch [57]ABSTRACT A water-washable inspection penetrant composition and processin which a low-solubility fatty oil is used as the penetrant vehicle.The solvent liquids of the invention provide enhanced stability ofpenetrant en trapments in surface flaws, so as to increase the allowabletime interval of wash water contact before an excessive depletion of theentrapment occurs. The flaw detecting capability of the water-washablepenetrant is thereby improved.

1 Claim, No Drawings WATER-WASI-IABLE INSPECTION PENETRANT EMPLOYINGTRIGLYCERIDES AND POLYGLYCERIDES OF FATTY ACIDS This application is acontinuation-in-part of my copending application Ser. No. 482,465, filedJune 24, 1974 for Enhanced Stability Water-Washable PenetrantComposition and Process Therefor.

The invention relates to inspection penetrant materials. Moreparticularly, the invention relates to waterwashable inspectionpenetrant compositions which exhibit enhanced values of indicationstability in the presence of wash water.

Heretofore, water-washable inspection penetrants have been comprisedessentially of a water-dispersible liquid carrier containing a dissolvedindicator dye. The liquid penetrant composition is selected orformulated so as to be readily soluble or self-emulsifiable in water.The indicator dye may be a visible-color dye or a fluorescent dye, butfor high sensitivity usage, fluorescent dyes are most generallyutilized.

In use, the water-washable penetrant is applied to parts to be testedfor the presence of surface flaws. After a suitable dwell time, duringwhich the penetrant enters any surface cracks which are present, thetest parts are washed with water to remove surface penetrant, leavingentrapments of the tracer-dyed liquid in the surface cracks. Followingthe wash-remover step, the test parts are dried and sometimes they aretreated with a fine-powder developer which acts to draw out penetrantentrapments to a point where they can be seen. In any event, the partsare inspected for the presence of surface flaw indications, using whitelight in the case of penetrants containing visible-color dye, or underblack light in the case of penetrants containing fluorescent dyes.Entrapments of dyed penetrant which are retained or developed on acoating of powder particles are detected by their visible color orfluorescence, as the case may be. Normally, the step of development isconsidered to be part of the inspection step in the process.

In the past, it has been the practice to formulate water-washablepenetrants in such a way that the compositions exhibit a feature of goodwashability, such that the surface penetrant is easily removed when testparts are washed with water. Acceptable penetrant formulations haveapparently been chosen for their ability to wash quickly so as toprovide a relatively clean test surface with a minimum background ofresidues of dye penetrant. I have discovered that existingwater-washable penetrants suffer from a serious drawback, in that theyare characterized by an excessive degree of emulsifiability orsolubility, such that in the process of wash-removal of surfacepenetrant, entrapments of penetrant in small, shallow surface flaws arealso removed, or at least are depleted to an excessive degree.

I have endeavored to improve the retention of entrapments in flaws byvarious means. One method which I have devised involves the formulationof socalled gel-forming penetrants, as exemplified by the teachings ofmy U.S. Pat. Nos. 3,282,843, 3,349,041, and 3,429,826, and my copendingapplication Ser. No. 127,681, filed Mar. 24, 1971, for InspectionPenetrant Compositions and Processes Employing BalancedSurfactant/Synergist Detergent Systems.

I have also devised various methods of inhibiting the solubility ofcertain kinds of penetrants (particularly the gel-forming penetrants),by adjustment of the detergent balance of the composition, byintroduction of certain solubility-inhibiting chemicals into thepenetrant or into the wash water, or by raising the temperature of thewash water above a critical point of solubility inversion, asexemplified by the teachings of my copending application Ser. No.163,643, filed July 19, 1971, for Method and Means for Improving FlawEntrapment Efficiency in Water-Washable Inspection Penetrants.

I have devised a technique for measuring the rate at which flawindications are depleted by the action of wash water, and I have foundit possible to assign values of Indication Depletion Time Constants tovarious materials such as water-washable penetrants, emulsifiers, andsolvent removers. In essence, my method of evaluation involves themeasurement by photoelectric means, of the loss of brightness of astandardized pattern of indications during the course of removerapplication, in the present case, the remover being water. The methodyields, for each water-washable penetrant, a time constant which is ameasure of the time in seconds of wash water contact required to depletethe effective magnitude of the flaw entrapment to 50% of its initialvalue. In some cases it may be preferred to state the time constant interms of the time in seconds of wash water contact required to depletethe brightness of an indication to 50% of its initial value.Measurements of Indication Depletion Time Constants are made using astandard cracked panel having a pattern of closely spaced cracks orrandomly distributed cracks of known effective magnitude.

I have found that the measured rate of indication depletion depends inpart on the magnitude of the cracks in the testing panel. I have madeand tested various kinds of testing panels in which I have been able togenerate crack defects having effective magnitudes varying from lessthan a micron up to 20 or 30 microns, and where the depth-width ratio ofthe cracks may vary from about 3 up to to 1. For many types of penetrantmaterials, it is practical to determine depletion time constants using acracked anodic panel of the types described and claimed in my U.S. Pat.Nos. 3,785,936 and 3,791,198, in which the cracks are about 20 micronsdeep and 6 microns wide.

The significance of the Indication Depletion Time Constant is that incases where processing conditions require a prolonged contact time ofthe wash water with the test surface, the Indication Depletion TimeConstant must be large, otherwise indications may be lost, By using themethods which I have devised, and which have become standard proceduresunder Air Force MIL-Specifications and industrial specifications, I havebeen able to assign Indication Depletion Time Constants to penetrantprocess materials, and have thus been able to assign ratings of relativeindication stability for such materials. It turns out that IndicationDepletion Time Constants for typical water-washable penetrants (using acracked anodic panel for example) fall in the range of from about 3 to10 seconds, while for certain of the above-mentioned gel-formingpenetrants, time constant values may be as high as 40 seconds.

While Indication Depletion Time Constant values in the range of 3seconds up to about 40 seconds are suitable for most industrialinspection requirements, there are numerous cases where it is necessaryto obtain a considerably higher degree of indication stability,

as might be provided by water-washable penetrants having IndicationDepletion Time Constants in the range of from about 40 seconds up to asmuch as 6000 seconds. One such inspection application is in the study ofinter-crystalline separations in plated surfaces, or ceramics. Anotherapplication is in the testing of molybdenum disilicide heat resistantcoatings for the presence of irregularities and discontinuities. In anyof these applications, and others, which require extremely high flawdetection sensitivity combined with an extremely high degree ofindication stability, it is essential that the water-washable penetrantshall resist the leaching of wash water during the time normally takenfor the wash step.

The principal object of the invention, therefore, is to providewater-washable inspection penetrant compositions with features ofenhanced flaw indication stability in the presence of wash water.

Another object of the invention is to provide a method of adjusting andcontrolling the Indication Depletion Time Constant value of awater-washable penetrant to a point within the approximate range of fromabout 40 seconds up to about 6000 seconds.

These and other objects of the invention will be in part be obvious andwill in part become apparent from the following description thereof.

I have discovered a family of solvent liquids which satisfy therequirement of high values of Indication Depletion Time Constant, and Ifind that such solvent liquids may be suitably defined as solventliquids which are soluble in water or compatible with water to theextent of from slightly less than 0.01% up to about 3%. If a solventliquid has a water solubility or compatibility much lower than 0.01%,then penetrant formulations using such liquid may exhibit an undulylarge depletion time constant, making wash removal of unwantedbackground indications excessively difficult. On the other hand, if thecompatibility with water of the solvent liquid is much greater than 3%,then the depletion time constant becomes small, to the point where thereis no advantage gained over materials already available which providedepletion time constants up to about 40 seconds.

It will be understood that the term compatibility with water refers toeither the solubility of a liquid in water or the solubility of water inthe liquid. It appears that the removal of penetrant entrapments fromcrack defects by washing with water takes place by a mechanism ofdiffusion of the two liquids, penetrant and water, into each other, andwash-removability of penetrant may take place at an acceptable rateprovided that the solubility of water in the penetrant or penetrant inwater fall within the above-stated percentage range. The percentagerange of water compatibility of from slightly less than 0.01% up to 3%is given merely to indicate the physical-chemical property (with respectto water solubility) of the solvent liquids which are suitable for thepurpose of the invention.

The penetrant compositions of the invention are comprised essentially ofone or more low-solubility liquids drawn from the group to be describedand identified below, the low-solubility liquids being selectivelyemployed, singly and in combination. When so used, these liquids willprovide Indication Depletion Time Constants within the range of about 40to 6000 seconds. Among the various solvent liquids which are suitable asingredients in the water-washable penetrants of the invention are:

Cottonseed oil,

Palm kernel oil,

Peanut oil,

Coconut oil,

Linseed oil,

Olive oil,

Soybean oil,

Castor oil,

Sunflower seed oil,

Rape seed oil,

Safflower oil,

Lard (grease),

Tallow,

Fish oil,

Sardine oil, and

Whale oil.

All of the foregoing oils, fats and greases fall in the same chemicalcategory, being triglycerides or polyglycerides of fatty acids, such asoleic acid, linoleic acid, linolenic acid, etc. Some of the materialsare solid at room temperature, but become liquid at slightly elevatedtemperatures. They are all considered to be water-insoluble, but I havediscovered that they are in fact sufficiently soluble in water,particularly at elevated temperatures, so as to permit wash-removal inthe water-washable inspection penetrant process.

I have found that it is possible to extend the polyglyceride oils of theinvention with an inexpensive aliphatic mineral oil, for purposes ofcost saving, or for purposes of reducing the viscosity of the penetrantcomposition. Normally, aliphatic mineral oils are not compatible withthe polyglyceride oils of the invention, and yield hazy mixtures whichseparate on standing. However, I have discovered that a small amount ofa suitable solvent coupler may act to couple the polyglyceride oil withthe mineral oil to form a clear solution. For example, in testingmixtures containing 20 ml. of castor oil and 100 ml. of a light mineraloil (Chevron No. 2 Absorption Oil), I have found that clear mixtures areobtained by the addition of 5 ml. of diethylene glycol monobutyl ether,or 4.5 ml. of dibutyl phthalate, or 3 ml. of isodecanol. In all cases,where the polyglyceride oil of the invention is extended by means of alight mineral oil, I find that the flaw detection capability of thepenetrant composition using such an extended vehicle is about the sameas is obtained by use of pure polyglyceride oil. This feature ofsimilarity is evident at concentrations of the mineral oil extender inthe penetrant vehicle up to or more. I have noticed that the actualvalue of Indication Depletion Time Constant which is characteristic of agiven penetrant composition of the invention may vary as theconcentration of indicator dye is varied. Since the flaw detectioncapability, or sensitivity, of an inspection penetrant increases as theindicator dye concentration is increased, it follows that for acomposition which utilizes a given solvent liquid of the invention, theIndication Depletion Time Constant will change as the sensitivity level(or dye concentration) is changed.

For example, if castor oil is utilized as the carrier liquid, and ifdifferent concentrations of fluorescent dye are tested, corresponding torelatively low up to relatively high sensitivity levels, as such levelsare known in the art, then Indication Depletion Time Constant values maybe obtained ranging from about 200 seconds for the low sensitivitycomposition up to about 10,000 seconds'for the high sensitivitycomposition. It will be understood that the rate of solution, and theconsequent Indication Depletion Time Constant, may be varied andadjusted by adjusting the temperature of the wash water. Depletion TimeConstants are reduced as the water temperature is increased, partlybecause the solubility of the oil increases, and partly because theviscosity of the oil becomes lower and effects of diffusion become morerapid.

I have found that the Indication Depletion Time Constants of thecompositions of the invention may be conveniently reduced and adjustedto desired values by the addition of an appropriate amount of awater-soluble solvent coupler. For the purpose of this specification,the designation solvent coupler shall be meant to include water-solublealcohols and glycol-ethers. Among the various solvent couplers which aresuitable for use as additives for reducing the Indication Depletion TimeConstant are the following:

methanol,

ethanol,

butanol,

isopropanol,

l-propanol,

Z-butanol,

ethylene glycol monobutyl ether,

ethylene glycol monomethyl ether,

ethylene glycol monoethyl ether,

diethylene glycol monoethyl ether,

diethylene glycol monomethyl ether,

diethylene glycol monobutyl ethe butoxytriglycol,

methoxytriglycol,

ethoxytriglycol, and

l-butoxyethoxy-2-propanol.

Any of the above-identified solvent couplers may be included in thecompositions of the invention at concentrations ranging from zero up toabout 40% relative to the low-solubility solvent liquid of theinvention, the proportional amount used depending on the dye sensitivitywhich pertains, the particular solvent which is used, and the desiredIndication Depletion Time Constant.

Visible-color or fluorescent indicator dye concentrations in thecompositions of the invention may range from about 0.2% up to about 30%,in accordance with known practices.

Accordingly, a water-washable inspection penetrant composition of theinvention may be expressed by the following formulation, stated inweight percentages:

Low-solubility solvent liquid 30% to 99.8% Indicator dye .2% to 30%Solvent Coupler zero to 40% Although the invention has been describedwith reference to particular embodiments thereof, it will be understoodthat various changes and modifications Low-solubility solvent liquid 30%to 99.8% Indicator dye .2% to 30% Solvent coupler zero to 40% saidlow-solubility solvent liquid being at least one member selected fromthe group consisting of:

Cottonseed oil, Palm kernel oil, Peanut oil, Coconut oil, Linseed oil,Olive oil, Soybean oil, Castor oil, Sunflower seed oil, Rape seed oil,Safflower oil, Lard, Tallow, Fish oil, Sardine oil, and Whale oil, andsaid solvent coupler being at least one member selected from the groupconsisting of:

Methanol, ethanol, butanol, isopropanol, l-propanol, 2-butanol, ethyleneglycol monobutyl ether, ethylene glycol monoethyl ether, ethylene glycolmonomethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether, diethylene glycol monobutyl ether, butoxytriglycol,methoxytriglycol, ethoxytriglycol, and l -butoxyethoxy-2-propanol, saidlow-solubility solvent liquids being selectively employed singly and incombination.

1. IN A WATER-WASHABLE INSPECTION PENETRANT PROCESS IN WHICH AWATER-DISPERSIBLE DYED LIQUID PENETRANT IS APPLIED TO TEST PARTS,SURFACE PENETRANT IS REMOVED BY WASHING SAID TEST PARTS WITH WATER, ANDSAID PARTS ARE INSPECTED FOR RESIDUAL ENTRAPMENTS OF PENETRANT LIQUID INSURFACE FLAWS, THE IMPROVEMENT WHEREIN SAID WATER-WASHABLE PENETRANTCONSISTS ESSENTIALLY OF THE FOLLOWING FORMULATION, STATE IN WEIGHTPERCENTAGES: